So for the behind the back pass, your hoop is going to stay mostly horizontal. You're going to start with the hoop in front of you, thumbs together, palms down. You're going to let go with one hand, swing the hoop around to your side behind your back.
Now, when the hoop gets behind you, you're going to grab pinky to pinky, palms down. Let go with the other hand, and bring the hoop around. So then you just repeat the same thing in front.
Behind the back, palms down, thumbs together, palms down. I'll show that from behind my back.
You can switch directions. My grip is not very tight at all. Whenever the hoop has momentum, you should just have a very, very loose grip. If I were to stop spinning, the hoop would just hang really, really loosely in my fingers. So, as I give it momentum, it swings horizontally on its own. Sometimes my thumb doesn't even touch the hoop.
That's how you do the behind the back pass.